Alexander A. Afonenko

Regular-pulsation asymmetric multiple-quantum-well heterostructure laser radiator

Regimes of regular pulse generation at remote optical wavelengths in asymmetric quantum-well heterostructure lasers have been examined in detail. Influence of the heterostructure parameters and pump current density on frequency, duration, and magnitude of light spikes and on phase shift between pulses of radiation at different wavelengths has been studied. Design of optimal band energy structures for novel type of laser sources is proposed.

Current injection and recombination processes in asymmetric triple quantum well lasers

For lasers based on asymmetric quantum-well heterostructures comprising three different quantum wells and barrier layers with a complex potential profile, current carrier injection and radiation emitting processes have been considered. The analysis performed by using rate equations has shown that a regime of regular pulse generation at remote wavelengths is practicle. The radiation pulsation process is accompanied by oscillations of the carrier injection efficiency into quantum wells. At certain parameters of the laser structures it is possible to realize radiation bistable switching-on or the regime where relative powers at different wavelengths change with increasing the pump current. The injection efficiency has been determined by solving the Poisson equation and continuity conditions for electron and hole currents. Carrier tunneling through potential barriers between the quantum wells has been taken into account. Calculations have been performed for the GaAs - AlxGa1- xAs system.

Quantum-well lasers and amplifiers with a wide-tunable spectrum

A novel type of laser diodes and amplifiers based on asymmetric quantum-well heterostructures having a set of active layers of different thickness and/or compositions has been considered. In contrast to ordinary laser heterostructures, for such modified quantum-well systems, it is possible to change the gain spectrum in a wide range and to control the set of definite amplification frequencies due to the selecting of the width and composition of quantum wells and barrier regions and of their doping and arrangement as well. New heterostructure schemes for tunable spectrum light-emitting sources have been proposed.

Broadening effects on emission spectra of the superlattice QC structures

Numerical calculations of the energy levels and wave functions for superlattice quantum cascade (QC) structure emitted in the middle infrared range are performed. The comparative analysis of the gain and radiative recombination spectra for the different broadening models is made.

Quantum-dimensional lasers with weak temperature dependence of the output power

An injection laser configuration based on asymmetric quantum-dimensional heterostructure with inhomogeneous excitation of quantum wells (QW) is proposed. This configuration allows one to substantially reduce the temperature dependence of the output power. It is demonstrated that the relative variation of the lasing power at room temperature can be less than 1% per 10°C.

On spectral line broadening in quantum-well heterostructure lasers

Theoretical analysis of the emission line broadening in quantum-well lasers is carried out taking into account the Coulomb interaction of current carriers in the approach of two-dimensional electron-hole gas. The principal idea of the used method consists in the determination by means of the perturbation theory for many-body systems the functional behavior of tails of the emission line and in the subsequent extrapolation of the central part of the line according to a normalization requirement. Based on the obtained in the parabolic band approximation analytical shape function for the homogeneously broadened spectral line, the influence of various factors on the optical spectrum is analyzed. An explanation of the experimental data, including the spectral line asymmetry and the linewidth change versus temperature and power excitation, is given. Results of the numerical calculations are presented for quantum-well heterostructure laser diodes in the GaInAsSb-AlGaAsSb-GaSb system. Spectra of luminescence and gain in dependence on the quantum well width, temperature, and excitation level are examined. Spectrum transformation in the long-wavelength range and tuning curves for the GaSb-based laser emitters are also discussed. New possibility to overlap the spectral emission diapason of 2.2-2.9 μm is examined due to asymmetric multiple-quantum-well heterostructure configuration of the active region.

Gain spectra and optical transition probability in doped quantum well heterostructures

In the work we investigated the influence of the dimensional quantization on the probability of optical transitions with no k-selection rule. It is shown that calculations of the recombination rate and gain coefficient will be inaccurate if they are performed with using the probability of optical transitions determined for bulk semiconductors. Successive examination of radiative transitions with no the k-selection rule leads to a qualitative coincidence of the dependence of the spontaneous recombination rate on the quantum well width with the results obtained in the model of direct transitions.With the suppression of the constant injection efficiency the inversion current value is practically independent of the quantum-well layer thickness. Various approaches for the calculation of the spontaneous recombination rate are discussed.

Nonlinear electron-optical processes in asymmetric structures with quantum wells

Theoretical consideration of lasing regimes of asymmetric semiconductor heterostructures has been made. The conditions for bistable power switching and periodical radiation pulsations have been determined. The efficiency of injection of current carriers into quantum wells has been investigated. Doping levels of the layers forming the asymmetric heterostructure and its band configuration to realize the request inhomogeneous excitation of the quantum wells have been defined. The asymmetric heterostructure waveguide properties have been considered and the optical confinement factor for various lasing modes has been established. Calculations have been performed for the GaAs-AlxGa1-xAs system.

Radiation oscillation processes in quantum-well heterolasers

The transient radiation oscillation process and generation instabilities in quantum-well laser systems are investigated in detail. A novel type of laser with quantum-well layers of various thickness is considered. The conditions for lasing switching with increasing the excitation current and for regular optical pulse generation have been determined. The calculations have been performed for the GaAs-AlGaAs system. The developed mathematical models and rate equations can be used to describe dynamics of laser action in quantum-well systems on other materials too.

Stability criterion for Fabry-Perot semiconductor laser with external feedback

We present theoretical and numerical analysis of stability of Fabry-Perot semiconductor laser with external optical feedback on the basis of wave equation. The analytical expressions for stability criterion and modulation part of photon density have been obtained taking into account singing of radiation in external cavity. The bounds of adaptability of equation based on slowly varying amplitude approximation are described.